Field of the Invention
The present invention is related to a novel cured-in-place pipe (CIPP) process utilizing a curable epoxy-anhydride thermoset system.
Description of Background and Related Art
Underground sewer pipes, potable water pipes, and other pipes fracture with use and age. Repair of these leaking and damaged pipes is time consuming and expensive as it involves excavation and replacement of these damaged pipes. Cured-in-place pipe (CIPP) technology was first utilized in the United Kingdom in 1971, and introduced to the North American market in the late 1970's. Over the next 20 years this technology revolutionized the sewer pipeline repair industry, providing a reliable solution to rehabilitating sewer pipelines without the need to excavate. There are two used processes for cured-in-place pipe applications: “Inversion Installation Method” and “Pull-in Installation Method”. The most common is the “Inversion Installation Method” and the process involves impregnating a flexible non-woven felt liner with the curable thermoset composition, followed by inverting the impregnated non-woven felt liner into an existing (host) pipe, and curing of the impregnated felt liner within the host pipe. The CIPP process is classified as rehabilitation or renovation because it forms a new hard inner pipe within and adhering to the existing host pipe.
There are three types of thermoset systems commonly used for this application:                Polyester—commonly used in sewer applications,        Vinyl ester—used in severe duty, industrial and special waste applications, and        Epoxy-amine thermosets—commonly used in potable water and pressure pipe applications.        
The traditional polyester system remains the lower cost workhorse of the industry. Although epoxy resins have been used to protect and repair all types of infrastructure for the past 75 years, their use in underground rehabilitation was limited due to handling constraints (a relatively shorter pot-life) and high cost. Although epoxy-amine thermoset systems are superior to polyesters for properties like shrinkage, adhesion, no presence of solvents like styrene, mechanical properties, and chemical resistance, their main draw-back is the shorter pot-life which makes it difficult to work in CIPP applications. Epoxy-amine thermosets have therefore been generally reserved for limited use in high end applications like aggressive municipal and industrial wastewater applications.
Pot-life is a measure of the working time in minutes during which the felt liner in a cured-in-place application can be impregnated with a thermoset resin system, inverted, and cured properly in the host pipe. A good pot-life for a successful CIPP application is greater than 5 hours. Polyesters and vinyl ester thermosets can manage this pot-life. Epoxy-amine thermosets can barely meet this requirement as their pot-life ranges from 30 minutes to barely 5 hours and sometimes under special conditions such as keeping it at a cooler temperature. Therefore, an epoxy thermoset system with a longer pot-life would be useful and desired for CIPP applications.